During the last 20 years, the carbonated beverage bottle industry has shown an increasing demand for the PET bottles, due to its lower weight and the fact the PET bottles show a higher rupture-resistance during the transportation, storage and handling of the carbonated beverages. The polymer known as bottle PET can be anyone of polyesters or copolyesters made with o-, m- or p-bencendicarboxilic acids. Those polymers are produced through the polycondensation reaction of those acids and/or its anhydride and/or its dimethyl esters with different glycols such as ethylene glycol and/or diethylene glycol and/or 1,4-bis(hydroximethyl)cyclohexene, also known as dimethanol-cyclohexane.
Carbonated beverage market distinguishes between two types of PET bottles: returnable and non-returnable bottles. After its use, empty non-returnable PET bottles are discarded to the garbage box, from where must be collected, sorted and cleaned for its recycling or otherwise land-fill disposed. On the other side, the U.S. Pat. No. 5,148,993 discloses that the returnable bottles are reused several times (3 to 5 for example) till the bottles separates them from service. The bottles are then crushed and/or grinded and then stored waiting for the polymeric material to be recycled. If the waste polymeric material is not recycled it is discarded as a non-biodegradable solid-waste to be accumulated in some place of the biosphere; otherwise they must be incinerated. Both, the accumulation and incineration are activities regarded as negative and noxious to the environment.
In some of the main industrial countries, with a relatively high rigid-polyurethane consumption, a process has been developed to transform the PET bottle polymer into a polyol of functionality equal to 2, which is useful in the production of polyurethane foams, by the depolymerization and transesterification of the polyester with diethyleneglycol, as disclosed in the U.S. Pat. No. 4,469,824. In the U.S. Pat. No. 5,095,145 terephthalic acid is produced, having developed a process for the production of terephthalic acid through hydrolysis of the bottle PET. In this process the steps of purification are delicate and complicate.
A theoretical solution exists for recycling clean waste product or intermediate wastes from the fiber grade polyester production process, through the depolymerization with low molecular weight alcohols, although those process were not economically feasible, since they implicated several steps of reaction and the stoichiometric raw materials yield was relatively low. For example, the U.S. Pat. Nos. 3,403,115 and 3,321,510 discloses process in this concern, but those innovations have not been exploited. Besides, those PET recycling innovations did not foresee any of the specific problems implied in the waste PET bottle recycling.
A need exists for a chemical process that treats molded plastic wastes, particularly of the polyesters made from the orto, meta and para-becendicarboxilic acids, known as bottle PET. This process should improve the yield of products from the raw materials and allows the recovery of high value chemicals, useful in ulterior manufacturing process. The process itself, as well as the waste material recycling purpose, should have acceptable ecological features.